1. Field of the Invention
This invention generally relates to digital communications and, more particularly, to a system and method for clock rate detection in clock and data recovery (CDR) and clock synthesis units (CSUs).
2. Description of the Related Art
Conventionally, system platforms provide an optical transceiver module with a reference clock and data at the reference clock multiplied rate. These rates are a selection of more than half a dozen rates which continue to increase as technology moves forward. The module is required to operate at the given data rate without any system setup communication. If this setup communication protocol was provided and all modules and systems spoke this protocol, then data rate acquisition would be relatively easy. However, this is not the case, as modules and system platforms do not communicate, data rate information between each other.
Some prior art CDR and CSUs optical interface data rates must be set manually, or user-selected prior to being placed into a system platform that supplies a reference clock. One undesirable alternative is a system platform that provides a single data rate that is not standardized among all platform developers and module vendors. A second alternative is to use CDR and CSUs capable of generating their own reference clocks and acquiring a non-predetermined data rate. However, this capability would add to the cost and complexity of the units. A third alternative would be to use CDR and CSUs with a control signal port able to communicate with the system platform for the purpose of a data rate already predetermined by the system platform. However, as mentioned above, no protocol exists for communications between CDR/CSU transceiver and a system platform.
Alternately, a CDR or CSU may be used without a reference clock, but such units are likely to provide a poor level of performance. As another alternative, a wide band single VCO could be used that can be tuned to operate at any possible data rate, but again, the level of performance is likely to be poor.
It would be advantageous if a CDR or CSU could be made to operate at a non-predetermined data rate without the complexity of auto-frequency acquisition or special, system platform communications.